1. Field of the Invention
The invention relates to a system for the quantization of signals comprising a transmitter section and a receiver section, the transmitter section comprising quantizing means, a difference producer and filter means, an input signal and a quantized output signal which is derived from the quantizing means, and functions as a feedback signal being applied to the difference producer and a signal derived from the output signal of the difference producer being applied to the quantizing means, the latter serving to quantize the level of the signal derived from the output signal of the difference producer in a plurality of quantizing levels in order to produce a quantized output signal, filter means being connected in the path of the input signal for relatively influencing the spectrum of the quantizing noise with respect to the spectrum of the input signal.
The invention may be employed in A/D and D/A-conversion and the conversion of a digital format into another digital format (D/D-conversion). Generally, the invention is employed in those signal processing methods in which, as an intermediate step, the number of quantizing levels of a signal is reduced and the sampling rate thereof is increased.
2. Description of the Prior Art
From the publication, IRE Transactions on Communication Systems, December 1962, pages 373-80, (reference D.1), it is known that quantizing noise can be reduced by a combination of feedback around the quantizer and increase of the sampling rate.
It is furthermore known from the publication, IEEE Transactions on Circuits and Systems, July 1978, pages 448-60, (reference D.2) that the ultimate signal-to-noise ratio in a DPCM feedback coder is determined by the noise of the A/D converter and the noise resulting from the threshold inaccuracy of the D/A converter included in the feedback loop. Said latter noise contribution reduces the gain in signal-to-noise ratio which can be achieved by the combination of the feedback around the quantizer and the increase of the sampling rate.